Science快訊：今日出版（03年12月12日）Science一篇報(bào)道揭示了人與黑猩猩基因組間的比較學(xué)研究,。
盡管經(jīng)過(guò)了幾十年的研究，遺傳學(xué)家仍然沒有破解人類何以為人之謎,。人類和我們的近親黑猩猩,，幾乎有著完全一樣的DNA。但一項(xiàng)新研究揭示了黑猩猩與人類基因組之間的關(guān)鍵差異,。
<img border="0" src=http://www.ebiotrade.com/newsf/yjcg/images/2003121111.jpg align="left" width="162" height="255">
加州賽萊拉診斷公司的遺傳學(xué)家Michele Cargill和他的同事檢查了7600個(gè)小鼠,、人類與黑猩猩共有的基因，并根據(jù)每個(gè)物種的正常突變速率篩選出堿基變異超過(guò)預(yù)想的基因,。他們得出結(jié)論,，有1547個(gè)人類基因和1534個(gè)黑猩猩基因經(jīng)歷了相對(duì)較快的變化，這些變化可能賦予物種更強(qiáng)的生命力,。小鼠的基因數(shù)據(jù)可以幫助研究小組確定這些基因隨著進(jìn)化時(shí)間是如何變化的,。
自5百萬(wàn)年前從最后一個(gè)共同祖先分化以來(lái)，黑猩猩和人類的許多與細(xì)胞信號(hào)傳導(dǎo)和氨基酸代謝有關(guān)的基因自都經(jīng)歷了巨變,。但基因的演變軌跡與兩個(gè)物種的信號(hào)和代謝演變并不相同,，這說(shuō)明二者遭遇的是不同的自然選擇壓力。在人類中,，有27到48個(gè)嗅覺蛋
白以及21個(gè)聽力蛋白中的3個(gè)顯示出顯著的變異加速，而黑猩猩并非如此,。相反,，黑猩猩的中胚發(fā)育基因和骨骼結(jié)構(gòu)基因發(fā)生的變化卻更多,。
人類嗅覺基因的快速進(jìn)化令人困惑不解。由于人類不再嚴(yán)重依賴他們的嗅覺來(lái)生存,，因此有人認(rèn)為嗅覺基因的變異沒有影響甚至有負(fù)面影響,。但這項(xiàng)新研究表明,，一些嗅覺基因的進(jìn)化有積極意義：它們的改變似乎是人類進(jìn)化過(guò)程中的選擇。這些基因促進(jìn)了某些飲食改變或機(jī)理了性選擇,，研究的作者之一,、紐約康奈爾大學(xué)的群體遺傳學(xué)家Andrew Clark解釋說(shuō)。
這項(xiàng)研究發(fā)表在12月12日期的《Science》上,，是通過(guò)基因組學(xué)方法識(shí)別“人性”的重要起點(diǎn),，加州大學(xué)圣地亞哥分校的生物學(xué)家Ajit Varki稱贊道,。他補(bǔ)充說(shuō)，將人類和黑猩猩的基因與比小鼠親緣關(guān)系更近的物種的基因組進(jìn)行比較,，如另一種類人猿,，將會(huì)揭示更多定義靈長(zhǎng)類進(jìn)化樹分支的基因。
Original report:
Despite decades of study, geneticists don’t know what makes humans human. Humans and our kissing cousins, chimpanzees, share practically all of our DNA. But new research reveals key differences between chimp and human genomes.
Hear no evil. Changes in genes for hearing, olfaction, and speech helped prompt human evolution.
CREDIT: PAT POWERS AND CHERRYL SCHAFER/GETTY IMAGES/DIGITAL VISION
Michele Cargill, a geneticist at Celera Diagnostics in Alameda, California, and her colleagues examined 7600 genes shared by chimps, humans, and mice, identifying those that had more than the expected number of base changes, given the normal mutation rates in each species. They concluded that 1547 human genes and 1534 chimp genes had experienced relatively rapid changes that likely endowed a survival advantage. The mouse data helped the team determine how the genes had changed over evolutionary time.
In both chimps and humans, many genes involved in cell signaling and amino acid metabolism have undergone major changes since the time of the species' last common ancestor 5 million years ago. But the genes didn’t follow the same track in the two species, suggesting that they faced different pressures from natural selection. In humans, 27 of 48 olfactory proteins and three of 21 hearing proteins showed significant accelerated change, whereas that was not true in the chimp. In contrast, the chimp’s genes for mesoderm development and skeletal structure had changed more.
The rapid evolution of olfactory genes in humans is puzzling. Because humans no longer rely strongly on their sense of smell to survive, any changes were assumed to have had no effect or a negative effect. But the new study suggests that some olfaction genes have been evolving in a positive way: Their changes appear to have been selected for during human evolution. The genes may have promoted certain dietary changes or informed sexual selection, says co-author Andrew Clark, a population geneticist at Cornell University in Ithaca, New York.
The work, reported in the 12 December issue of Science, “is a valuable start to the genomic approach to identify ‘humanness,’ ” says Ajit Varki, a glycobiologist at the University of California, San Diego, who adds that comparing human and chimp genes to the genome of a closer relative than mice, such as another great ape, would reveal even more genes that defined the branches of the primate family tree.
--ELIZABETH PENNISI
Original article:
Inferring Nonneutral Evolution from Human-Chimp-Mouse Orthologous Gene Trios
Andrew G. Clark, Stephen Glanowski, Rasmus Nielsen, Paul D. Thomas, Anish Kejariwal, Melissa A. Todd, David M. Tanenbaum, Daniel Civello, Fu Lu, Brian Murphy, Steve Ferriera, Gary Wang, Xianqgun Zheng, Thomas J. White, John J. Sninsky, Mark D. Adams, and Michele Cargill
Science Dec 12 2003: 1960-1963. [Abstract] [Full Text] [PDF] [Supporting Online Material]
Related articles:
R. Sakate et al., Genome Res. 13, 1022 (2003).[Abstract/Free Full Text]
Y. Satta, J. Klein, B. Takahata, Mol. Phylogenet. Evol. 14, 259 (2000).[CrossRef][ISI][Medline]
